1. Field of the Invention
This invention relates generally to auxiliary power units, and more particularly to an auxiliary power unit that integrates with a vehicle's existing air conditioner and heater.
2. Description of Related Art
Auxiliary power units that provide heating or cooling to a vehicle are known in the art. Prior art auxiliary power units are adapted to be used in class 8 vehicles, and include separate heating and air conditioning components for heating or cooling the truck while the truck engine is turned off. Class 8 trucks have a gross vehicle weight rating (GVWR) of over 33,000 pounds (i.e., tractor trailer trucks).
Brummett, U.S. Pat. No. 7,150,159, for example, teaches an auxiliary power unit that is adapted for use in large class 8 tractor trailer trucks. The auxiliary power unit includes an auxiliary engine that directly drives an air conditioning compressor within the auxiliary power unit. Importantly, the unit also includes a condenser, a radiator, a fan to cool the radiator and condenser, and other components necessary to cool the vehicle. The auxiliary power unit does not use the air conditioning components already installed in the vehicle, but requires the purchase and installation of a second set of these components.
Wurtele, U.S. 2006/0131885, teaches an auxiliary power unit that is also adapted for larger, class 8 tractor trailer trucks, and which also requires the purchase of a second air conditioning and heating system. The air conditioning and heating systems are powered by a generator located in the auxiliary power unit.
Greer, U.S. Pat. No. 4,756,359, also teaches an auxiliary air conditioning and heating system for vehicles. Greer teaches an engine, alternator, water pump, air conditioning compressor, and heat exchanger mounted on the tractor of a tractor trailer truck or other large vehicle. The main engine of the truck operates the existing truck air conditioning and heating system in a normal manner when the main engine is running. When the main engine of the truck is not operating and the smaller engine of the auxiliary power plant is operating, the truck air conditioning and heating system is operated by the auxiliary power plant. The heat exchanger of the auxiliary power plant then utilizes the heat of exhaust gases generated by the auxiliary power plant engine to warm the truck engine during the time it is not operating so that easy starting of the truck engine is made possible even in very cold weather. The exhaust gases from the auxiliary engine are also utilized to heat the lubricating oil of the main engine. When desired, an external load is applied to the crank shaft of the auxiliary engine to increase the heat output generated by the auxiliary engine.
Vehicles that are smaller than class 8, and in particular class 5 specialty vehicles, typically have integrated air conditioning and heating systems; however, there are no auxiliary power unit that are adapted to these vehicles, and that integrate with these systems. There is a long felt need in the field for such systems, as many smaller specialty vehicles, especially government vehicles, tend to be left idling at work sites for long periods of time, rapidly wearing out the engine and other components.
The prior art teaches an auxiliary power units installed in class 8 tractor trailer trucks. However, the prior art does not teach an auxiliary power unit that is adapted for smaller vehicles, and which integrates with a vehicle's existing air conditioner and heater systems. The present invention fulfills these needs and provides further related advantages as described in the following summary.